1. Field of the Invention
This invention relates to radiation sensitive devices, such as a film, sticker or badge for monitoring a dose of high-energy radiations, such as ultraviolet (UV) radiation, electrons, X-rays, protons, alpha particles and neutrons utilizing radiation sensitive materials, such as diacetylenes.
2. Brief Description of Prior Art
High energy radiations, including those having energy higher than 4 eV, such as UV light, X-rays, gamma rays, electrons, protons, alpha particles, neutrons, and laser radiation are used for a variety of applications, such as sterilization of medical supplies and perishables, curing of coatings and cross-linking of polymers, recording of images and information, radiography, nondestructive testing and diagnostic and radiation therapy. Their exposure needs to be monitored. Electronic equipment for monitoring radiation is expensive. There is a need for a simple dosimeter which can be used for monitoring a very low dose to a very high dose, such as 0.1 rad to 10 megarads (Mrads) of radiation having energy of 4 eV to 100 MeV.
In the case of a terrorist attack with a radiological dispersion device often referred to as “dirty bomb”, an accident at a nuclear power plant or nuclear powered ship/submarine, or a nuclear explosion, the first responders and people affected by them want to know, “Did I receive a lethal exposure to ionizing radiation or will I be OK?” Medical personnel treating the victims need to quickly assess the radiation dose each individual has received to ensure that treatment is provided first to those who need it the most. We have developed a credit card-sized radiation dosimeter that answers those questions quickly and cheaply. The badge can be worn for months to years. When exposed to radiation from a “dirty bomb”, or nuclear detonation, the sensing material changes color providing the wearer or medical personnel instantaneous information on cumulative radiation exposure of the victim. It can take days to get that information by other methods.
The following is the list of some exposure limits and symptoms for various dosages of high energy radiation (mRem=millirem and mSv=milli Sievert):
Public dose limits due to licensed activities100 mRem/yearLumbar/spinal x-rays130 mRem/exposurePelvis/Hip x-ray170 mRem/exposureUpper GI series245 mRem/exposureCumulative Natural Background300 mRem/yearLower GI series405 mRem/exposureOccupational Exposure Limits for Minors500 mRem/yearOccupational Exposure Limits for Fetus500 mRemOccupational Limits-DDE5,000 mRem/yearOccupational Limits-SDE (skin)50,000 mRem/yearOccupational Limits-SDE (extremities)50,000 mRem/yearOccupational Limits-LDE (lens of eye)15,000 mRem/yearDiagnostic thyroid exam90,000 mRad/exposureTherapeutic thyroid exam1,000,000 mRad/exposureDose to cause acute radiation sickness~1000 mSvDose leading to a 50% chance of death>4500 mSvfrom acute symptoms
It is well established that high dose ionizing radiation can cause cancer. The effect and symptoms of a high dose are well known.
0 to 25 radsNo easily detectable clinical effect inhumans. However, at about 15 rads therecould be temporary sterility (Testis).25 to 100 radsSlight short-term reduction in blood cells.Disabling sickness not common.100 to 200radsNausea and fatigue. Vomiting if dose isgreater than 125 rads. Longer-termreduction in number of some types ofblood cells.200 to 300 radsNausea and vomiting on the first day ofexposure. Up to a two-week latent periodfollowed by appetite loss, general malaise,sore throat, pallor, diarrhea, and moderateemaciation. Recovery in about threemonths unless complicated by infection orinjury.300 to 600 radsNausea, vomiting, and diarrhea in first fewhours. Up to a one-week latent periodfollowed by loss of appetite, fever, andgeneral malaise in the second week.Followed by bleeding, inflammation ofmouth and throat, diarrhea, andemaciation. Some deaths in two to sixweeks. Eventual death for 50% if exposureis above 450 rems. Others recover in aboutsix months.Over 600 remNausea, vomiting, and diarrhea in the firstfew hours. Followed by rapid emaciationand death in 2nd week. Eventual death ofnearly 100%. High dose could lead todeath.
There is no doubt that radiation can cause cancer. The question is what level of radiation it takes to cause cancer. The risk for radiation exposure has been very widely studied. The general consensus of opinion for the induction of cancer by ionizing radiation is 10% increase in cancer rate/Sv when the dose is given over a short time with a decrease to 5% when the dose is protracted over an extended time period. One Sv is equal to 1000 mSv and one mSv is equal to 100 mRem. Therefore a 10% increase in cancer is related to a dose of 100,000 mRem with 5% if the dose is protracted over a longer period of time. If one receives a harmful level of dose of ionizing radiation (e.g., 1-1,000 rads), one needs to know immediately so that proper medical care can be given. Dosimeters for dose higher than a few thousand rads have been reported (Standards on Dosimetry for Radiation Processing, ASTM International, 100 Barr Harbor Drive, West Conshohochen, Pa., 2002). However, they are not in form of a badge. There is a need for a radiation dosimeter in the form of a badge, bandage, tape, sticker, label, etc, which changes color instantly and wherein dose can be estimated from the intensity of the color using a color reference chart.
For monitoring high energy radiation, mainly two types of dosimeter badges are primarily used. One type contains a piece of silver halide film commonly known as a film dosimeter. The other contains a thermoluminescence material commonly known as a TLD dosimeter.
The main advantage of silver halide film is that very high final quantum yield and exposure can be stored permanently. However, silver halide film has many disadvantages and drawbacks: (a) making an emulsion of silver halide is a multi-step and expensive process, (b) the film requires protection from ambient light until fixed, (b) the developing and fixing processes are “wet” chemical based, and the concentrations of individual solutions and chemicals, time and temperature of developing and fixing must be strictly controlled. The badge needs to be sent to a processing lab for estimation of radiation dose exposure.
When a strong energy source (such as ionizing radiation) hits a thermoluminescence (TL) material, electrons are freed from some atoms and moved to other parts of the material, leaving behind “holes” of positive charge. Subsequently, when the TL material is heated, the electrons and the “holes” re-combine, and release the extra energy in the form of light. The light intensity can be measured, and related to the amount of energy initially absorbed through exposure to the energy source.
Neither the TLD nor the film dosimeters are instant. They need either developing or heating and expensive equipment to read the dose. The TLD type dosimeter can be read only one time. Once a TLD dosimeter is read, the dose information is lost for ever.
Hence, it is desirable to have a highly sensitive, self-developing, dry fixing film and dosimeter, which is not affected by ambient conditions, and which leaves a record of the result to confirm the dose. We have developed, such as film and dosimeter using radiochromic materials.
Any material, such as a diacetylene, a radiochromic dye, a mixture of leuco and/or pH sensitive dyes with an acid producing compound and the like, or mixture thereof, which undergoes at least one noticeable or monitorable change, such as change in color, fluorescence, opacity and magnetic resonance, is referred herein to as “radiation sensitive compound”, “radiation sensitive material” “radiochromic material” or “radiation sensitive formulation”.
One class of materials that can be used in the system comprises conjugated alkynes and are referred to as diacetylenes, R—C≡C—C≡C—R, where R is a substituent group. Diacetylenes polymerize in the solid state either upon thermal annealing or exposure to high-energy radiation [Adv. Polym. Sci., vol. 63, 1 (1984)]. The term diacetylene(s) is used herein to designate a class of compounds having at least one —C≡C—C≡C— functionality group. The solid monomers are colorless or white. The partially polymerized diacetylenes are blue or red. Polydiacetylenes appear metallic typically having a copper or gold color. Polydiacetylenes are highly colored because the “π” electrons of the conjugated backbone are delocalized. The color intensity of the partially polymerized diacetylenes is proportional to the percent polymer conversion. Diacetylenes which develop blue color are referred to as blue diacetylenes and those develop red color are referred to as red diacetylenes herein.
Diacetylenes are known to crystallize into more than one crystallographic modification or phase. A phase which polymerizes rapidly is referred to as an active phase or active form. A phase which does not polymerize is referred to as an inactive phase or inactive form. Some phases show little or no polymerization upon thermal annealing. Such phases are referred to as thermally inactive phases. A phase which polymerizes rapidly upon irradiation is referred to as a radiation active phase. By selecting a proper solvent system, some diacetylenes, such as diacetylene-344 [R—C≡C—C≡C—R where R═OCONH(CH2)3CH3] can be crystallized into a phase which would have extremely low thermal reactivity to provide long shelf-life and high radiation reactivity to monitor low dose, such as a few rads, by developing a noticeable color.
A number of patents have been issued on the synthesis and use of conjugated polyacetylenic compositions as radiation dosimeters, temperature monitors, and time temperature indicators.
The use of diacetylenes in photographic and other related arts is disclosed in several U.S. patents, such as, U.S. Pat. Nos. 3,501,297 and 3,679,738 (issued to Cremeans), U.S. Pat. No. 3,501,302 (issued to Foltz), U.S. Pat. No. 3,501,303 (issued to Foltz et al), U.S. Pat. No. 3,501,308 (issued to Adelman) and U.S. Pat. Nos. 3,743,505; 3,844,791 & 4,066,676 (all three issued to Bloom). These patents disclose dispersions in resin, gelatin, or gum matrices of certain diacetylene crystals for directly imaging photo-reactive compositions. Light exposed areas are evidenced by a color change.
Diacetylenes are not sensitive to visible, long wavelength, radiation. Luckey and Boer in U.S. Pat. No. 3,772,027 disclose a diacetylenic photosensitive element containing inorganic salts such as titanium dioxide, zinc oxide, cadmium iodide, and cadmium sulfide as sensitizers to make the element sensitive to visible radiation. Another similar patent (U.S. Pat. No. 3,772,028), issued to Fico and Manthey, discloses a photosensitive element sensitized to visible radiation by the addition of pyrylium salts including thiapyrylium and selenapyrylium salts. Amplification of poorly imaged crystalline diacetylenic compositions are obtained in U.S. Pat. No. 3,794,491, issued to Borsenberger et al. Faint images are enhanced through post-exposure irradiation. These patents describe formulations and processes for making diacetylenes sensitive to longer wavelength, lower energy, radiation, such as visible radiation so that the film can be used as a photographic film for visible light. U.S. Pat. No. 5,420,000 reports on the sensitization of diacetylenes to shorter wavelength, higher energy, radiation, such as UV, X-rays, electrons and alpha particles. Such sensitization to higher energy radiation is desirable for making, for example, diagnostic X-ray film.
Lewis, Moskowitz, and Purdy in U.S. Pat. No. 4,734,355 disclose a processless recording film made from crystalline polyacetylenic compounds. They also disclosed a process of dispersing crystalline polyacetylenic compounds in a non-solvating medium to a concentration of about 2% to 50% polyacetylene crystalline solids and aging the dispersion before drying on a substrate. The sensitivity of the obtained film is low and hence exposure of at least ten Gy of radiation is required to produce the image.
Guevara and Borsenberger describe, in U.S. Pat. No. 3,772,011, printout elements and methods using photoconductors and crystalline polyacetylenic compounds in contact with a photoconductive layer. Visible images are obtained when these layers are contacted with the application of an electric potential. In the absence of an applied potential, the elements described are stable under normal room-light handling conditions. Guevera et al., in U.S. Pat. No. 3,772,011, provides a diacetylenic composition, which undergoes direct image-wise photo-polymerization to a highly colored polymeric product when elaborated into a layer of micro-crystals contiguous to a photoconductive layer. Such polymerization takes place upon exposure during the application of an electric potential across the layers. In some cases, an organic photoconductor may be included in the layer of crystalline polyacetylenes.
Patel in U.S. Pat. Nos. 4,235,108; 4,189,399; 4,238,352; 4,384,980 has disclosed a process of increasing the rate of polymerization by cocrystallization of diacetylenes. Patel and others in U.S. Pat. Nos. 4,228,126 and 4,276,190 have described an inactive form of diacetylene for storing, and a method of rendering them active prior to use by solvent, vapor and/or melt recrystallization.
Mong-Jon Jun at el., U.S. Pat. No. 3,836,368 describe 2,4-hexadiyn-1,6-bis(n-hexyl urethane), referred to here in as “166”, which turns red upon short wavelength UV irradiation. They prepared a coating formulation by adding water to a solution of 166 in polyvinylpyrrolidone in methanol. U.S. Pat. No. 5,420,000 described a highly sensitive coating of 166. Although 166 is sensitive to UV radiation, the reactivity is not sufficient to use it for applications, such as diagnostic X-ray film.
In order to monitor a low dose one needs a relatively thick, e.g., more than about 25 microns, coating. The later mentioned patents don't describe a method or formulation for obtaining a thick coating, film, plaque and/or block and the processes of making them, which can be used for radiation monitoring and imaging, e.g., (1) personal dosimeter, (2) radiographic film and (3) imaging of radiation sources.
Silver halide film is not very sensitive to diagnostic X-ray radiation. X-ray images are amplified by placing the film between two fluorescence screens known as intensifying screens. Intensifying screens are luminescent materials and usually consist of a crystalline host material to which is added a trace of an impurity. Luminescence in inorganic solids usually originates at defects in the crystal lattice (Thomas F. Soules and Mary V. Hoffman, Encyclopedia of Science and Technology, Vol. 14, 1987, pp 527-545). The phosphor of the fluorescence screen absorbs X-rays and emits white light. Intensifying screens made with calcium tungstate phosphors have been in use since the time of Roentgen. Around 1972, a new phosphor, gadolinium oxysulfide was developed which emits in the green region and film sensitized to absorb green light was also developed. About the same time other phosphors, such as barium fluorochloride and lanthanum oxybromide, which emit in the blue region, were developed. A large number of phosphors have been reported in the literature including terbium activated rare earth oxysulfide (X2O2S where X is gadolinium, lanthanum, or yttrium) phosphors (T. F. Soules and M. V. Hoffman, Encyclopedia of Chemical Technology, Vol. 14, pp 527-545, 1981 and references quoted therein). Gadolinium and tungsten have very high atomic numbers and also have a high-energy absorption coefficient. The following combinations have been used for this purpose: GdOS:Tb(III), LaOS:Tb(III), LaOBr:Tb(III), LaOBr:Tm(III), and Ba(FCl)2:Eu(II). A number of patents e.g. U.S. Pat. Nos. 5,069,982; 5,173,611; 4,387,141; and 4,205,234 are representative and have been issued. Among the hundreds of phosphors reported, the literature search reveals that most of them are blue-, green-, or long wave-UV emitting phosphors upon excitation by X-ray. Some of them emit long wavelength blue light, for example, U.S. Pat. No. 4,719,033. No one has so far reported an X-ray screen with a short-wave UV emitting (e.g., wavelength shorter than 275 nm) phosphor.
Converters, or phosphors, are usually used as a screen in the form of a fine powder dispersed in a polymeric binder. The screens are placed in contact with the emulsion of silver halide film during X-ray irradiation. The prior art does not describe a converter/phosphor, which is in the form of a transparent coating being a solid solution or complex of a converter with a polymeric binder. The use of these converters in the under coat, radiation sensitive coat and topcoat of the device is also not described. The phosphors emitting short wavelength UV light can be used as a screen to amplify the radiation image.
U.S. Pat. No. 5,206,118, to Sidney et al, describes a color changing film made of a halogen containing polymer in which is dispersed an acid sensitive leuco dyes. When exposed to high energy radiation, it develops color. U.S. Pat. No. 5,451,792 discloses a device with color reference chart and radiation sensitive coating containing a leuco dye and halogen compound.
A card type dosimeter with a piece of radiochromic film is described in U.S. Pat. No. 6,232,610. A radiation indicator for monitoring radiation is described in U.S. Pat. No. 5,359,200. TLD type dosimeters for monitoring radiation are described in U.S. Pat. Nos. 5,177,363, 5,508,523, 6,127,685, 4,506,157, 4,975,589, 5,179,281, 4,346,511 and 5,083,031.